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by Gary Mann.

Cymap. How to model split exposures for Roofs, Ceilings and Floors by Gary Mann.

This example shows how to model a single floor or roof face which has both internal and external properties.

The simplified model consists of a ground floor area of 4x4m (16m2) and a first floor plan of 2x2m or 4m2. The outside heating design temperature is assumed to be -5oC and the room temperature to be 20oC in both rooms. These temperatures can easily be changed but have been chosen for simplified manual checking of Cymap outputs.

Purpose of this example is to show how the losses from the ground floor Roof & Ceiling will be 12m2 exposed roof and 4m2 internal ceiling.



  • Set up the DXF files in the usual manner.
  • Define the rooms as usual.
  • Next, we need to edit the Elements database, using the Tools\Elements\Roof section

  • Highlight the row containing the Roof properties, this will be show in highlighted text, and copy using Ctrl+C Copy command.

  • Next, choose the internal “Ceiling” materials and paste the copied Roof details using Ctrl+V.
  • You should now see the external roof sitting comfortably with the internal ceiling constructions.
  • Enter a description to remind yourself and others and for quality assurance purposes.
  • Edit the Internal Ceiling U value to the minimum allowed, e.g. 0.03 W/m2K
  • Select the ground floor by left click, to select the room and then right click and select “Face Data”.

  • Select the external Roof data that you pasted in previously and Untick the Auto Calculate the temperature difference button and add winter & summer Delta T’s according to the external conditions required e.g. Winter -5oC outside, 20oC inside = 25oC total.
  • 9. Click on the Ceiling Elements in the Face dialog and then use the “Add Element” button

  • Enter the relevant x & y coordinates of the internal section of the “Roof” and ensure that the reduced U value ceiling has been selected.

  • On moving onto the Energy program and selecting “Display\Heat Losses”, one can see the separate listing for the internal and external Roof\Internal Ceiling components.

  • From within the First Floor, one can see that the temperature loss through the internal floor is zero, because the temperature is the same in both rooms. If you were to edit any of the room temperatures then this positive or negative heat transfer would show!

You can download a zip file containing the above simplified project below.

Let me know if you found this helpful or have any suggestions for future blogs.